The present invention relates to novel cyclosporins, their use as pharmaceuticals and pharmaceutical compositions comprising them, as well as to processes for their production.
The cyclosporins comprise a class of structurally distinctive, cyclic, poly-N-methylated undecapeptides, commonly possessing pharmacological, in particular immunosuppressive, anti-inflammatory and/or antiparasitic activity. The first of the cyclosporins to be isolated was the naturally occurring fungal metabolite Ciclosporin or Cyclosporine, also known as cyclosporin A and commercially available under the Registered Trademark SANDIMMUN.RTM. or SANDIMMUNE.RTM.. Ciclosporin is the cyclosporin of formula A. ##STR1## where MeBmt represents the N-methyl-(4R)-4-but-2E-en-1-yl-4-methyl-(L)threonyl residue of formula B ##STR2## in which --x--y-- is --CH.dbd.CH-- (trans).
Since the original discovery of Ciclosporin, a wide variety of naturally occurring cyclosporins have been isolated and identified and many further non-natural cyclosporins have been prepared by total- or semi-synthetic means or by the application of modified culture techniques. The class comprised by the cyclosporins is thus now substantial and includes, for example, the naturally occurring cyclosporins A through Z [cf. Traber et al; 1, Helv. Chim. Acta, 60, 1247-1255 (1977); Traber et al; 2, Helv. Chim. Acta, 65, 1655-1667 (1982); Kobel et al, Europ. J. Applied Microbiology and Biotechnology, 14, 273-240 1982); and von Wartburg et al, Progress in Allergy, 38, 28-45, 1986)], as well as various non-natural cyclosporin derivatives and artificial or synthetic cyclosporins including dihydro-cyclosporins [in which the moiety --x--y-- of the MeBmt residue (formula B above) is saturated to give --x--y--=--CH.sub.2 --CH.sub.2 --]; derivatised cyclosporins (e.g. in which the 3'-O-atom of the MeBmt residue is acylated or a further substituent is introduced at the .alpha.-carbon atom of the sarcosyl residue at the 3-position); cyclosporins in which the MeBmt residue is present in isomeric form (e.g. in which the configuration across positions 6' and 7' of the MeBmt residue is cis rather than trans); and cyclosporins in which variant amino acids are incorporated at specific positions within the peptide sequence, e.g. employing the total synthetic method for the production of cyclosporins developed by R. Wenger--see e.g. Traber et al. 1, Traber et al, 2 and Kobel et al., loc. cit.; U.S. Pat. Nos. 4,108,985, 4,220,641, 4,288,431, 4,554,351, 4,396,542 and 4,798,823 European Patent Publications Nos. 34,567A, 56,782A, 300,784A, 300,785A and 414,632A; International Patent Publication No WO 86/02080 and UK Patent Publications Nos. 2,206,119 and 2,207,678; Wenger 1, Transpl. Proc., 15 Suppl. 1:2230 (1983); Wenger 2., Angew. Chem. Int. Ed. 24 77 (1985) and Wenger 3., Progress in the Chemistry of Organic Natural Products, 50, 123 (1986).
The class comprised by the cyclosporins is thus now very large indeed and includes, for example, [Thr].sup.2 -, [Val].sup.2 -, [Nva].sup.2 - and [Nva].sup.2 -[Nva].sup.5 -Ciclosporin (also known as cyclosporins C, D, G and M respectively), [3-O-acetyl-MeBmt].sup.1 -Ciclosporin (also known as cyclosporin A acetate), [Dihydro-MeBmt].sup.1 -[Val].sup.2 -Ciclosporin (also known as dihydro-cyclosporin D), [(D)Ser].sup.8 -Ciclosporin, [MeIle].sup.11 -Ciclosporin, [(D)MeVal].sup.11 -Ciclosporin (also known as cyclosporin H), [MeAla].sup.6 -Ciclosporin, [(D)Pro].sup.3 -Ciclosporin and so on.
In accordance with conventional nomenclature for cyclosporins, these are defined throughout the present specification and claims by reference to the structure of Ciclosporin (i.e. Cyclosporin A). This is done by first indicating those residues in the molecule which differ from those present in Ciclosporin and then applying the term "Ciclosporin" to characterise the remaining residues which are identical to those present in Ciclosporin. At the same time the prefix "dihydro" is employed to designate cyclosporins wherein the MeBmt residue is hydrogenated (dihydro-MeBmt) i.e. where --x--y-- in formula B is --CH.sub.2 --CH.sub.2 --. Thus [Thr].sup.2 -Ciclosporine is the cyclosporin having the sequence shown in Formula A but in which .alpha.Abu at the 2-position is replaced by Thr, and [Dihydro-MeBmt].sup.1 -[Val].sup.2 -Ciclosporin is the cyclosporin having the sequence shown in Formula A but in which the MeBmt residue at position 1 is hydrogenated and .alpha.Abu at the 2-position is replaced by Val.
In addition, amino acid residues referred to by abbreviation, e.g. Ala, MeVal, .alpha.Abu etc. are, in accordance with conventional practice, to be understood as having the (L)-configuration unless otherwise indicated, e.g. as in the case of "(D)Ala". Residue abbreviations preceded by "Me" as in the case of "MeLeu", represent .alpha.-N-methylated residues. Individual residues of the cyclosporin molecule are numbered, as in the art, clockwise and starting with the residue MeBmt or dihydro-MeBmt in position 1. The same numerical sequence is employed throughout the present specification and claims.
It is now well established that Ciclosporin acts by interfering with the process of T cell activation by blocking transcription initiation of IL-2, although the precise mechanism has not yet been elucidated. Ciclosporin has been shown to form a complex with a 17 kD cytosolic protein (cyclophilin) that occurs in many cell types and has been shown to be identical to peptidyl-prolyl cis-trans isomerase, an enzyme involved in protein folding. Up to now, however, it has not been clear whether binding to cyclophilin is directly correlated with immunosuppressive activity in cyclosporins, or indeed whether cyclophilin binding is itself a sufficient criterion for immunosuppressive activity.